The present invention relates generally to ferrules having a polished front surface and, more particularly, to ferrules having alignment features to facilitate the polishing of their front surfaces following the preassembly of the ferrules into connectors, as well as an associated jig and method for holding a ferrule during polishing operations.
Optical fibers are utilized for a variety of applications, including data transmission and the like. In order to interconnect the optical fibers, fiber optic connectors are mounted upon the end portions of the optical fibers, and pairs of the fiber optic connectors are thereafter mated. In order to provide an optical connection with the relatively low attenuation and the small return loss demanded by many modem applications, fiber optic connectors are generally designed such that fiber-to-fiber contact is established between the optical fibers upon which the respective fiber optic connectors are mounted. For example, fiber-to-fiber contact is preferably established between each optical fiber of a first fiber optic cable upon which a first fiber optic connector is mounted and the respective optical fibers of a second fiber optic cable upon which a second fiber optic connector is mounted, once the first and second fiber optic connectors have been mated.
In order to establish fiber-to-fiber contact, the front surface of the ferrule of each fiber optic connector must be precisely formed to ensure that the front surface is extremely smooth and planar and to minimize any angular errors relative to the optical fiber bores defined by the ferrule. In other words, the front surface of the ferrule is preferably formed to define a planar surface that extends perpendicular to the longitudinal axes of the optical fiber bores. By way of example, the front face of most ferrules must generally have an angular error of less than 0.2xc2x0 relative to the optical fiber bores to ensure that the optical fibers upon which the ferrule is mounted can be brought into dry physical contact with the optical fibers of another fiber optic connector.
Most ferrules are molded from a plastic material. Although the ferrules are typically molded to within relatively specific tolerances, the front surfaces of the ferrule are generally unable to be molded to have a sufficiently smooth front surface and to have a sufficiently small angular error. As such, the front surfaces of the ferrule must generally be polished after the ferrule has been mounted upon the end portions of the optical fibers. Not only does the polishing serve to smooth the front surface and to reduce the angular error of the front surface of the ferrule to within acceptable limits, such as less than 0.2xc2x0, but the polishing also serves to ensure that the ends of the optical fibers are properly positioned relative to the front surface of the ferrule, such as by either being flush with the front surface of the ferrule or by protruding by a predetermined amount relative to the front surface of the ferrule.
The front face of the ferrule is generally polished to have a predetermined angular relationship, such as 90xc2x0, with respect to the longitudinal axes of the optical fiber bores defined by the ferrule. Since the longitudinal axes of the optical fiber bores are inaccessible for use as a reference point or datum during polishing operations, ferrules are typically designed to have some other reference point or datum that has a predefined positional or angular relationship with respect to the longitudinal axes of the optical fiber bore. As such, the polishing of the front face of the ferrule can be done with respect to the datum that is accessible in order to appropriately polish the front face of the ferrule relative to the longitudinal axes of the optical fiber bores.
With respect to cylindrical single fiber ferrules, the outer diameter of the cylindrical shaft portion of the single fiber ferrule is typically used as the datum. The cylindrical shaft portion of a single fiber ferrule is an effective datum for polishing purposes for at least two reasons. First, the outer diameter of the cylindrical shaft of a single fiber ferrule has a predefined relationship with the longitudinal axis of the optical fiber bore, namely, the longitudinal axes of the optical fiber bore and the cylindrical shaft of the single fiber ferrule are usually coincident. Secondly, the outer diameter of the cylindrical shaft portion of a single fiber ferrule is required to be precisely formed since the outer diameter of the cylindrical shaft of a single fiber ferrule is also utilized to align the optical fiber upon which the ferrule is mounted with another optical fiber during the process of mating a pair of single fiber connectors. In this regard, the outer diameter of the cylindrical shaft portion of a single fiber ferrule is typically formed to within a tolerance of one micron.
In order to polish the front face of the single fiber ferrule, the cylindrical shaft portion of the ferrule is positioned within a precision bore defined by a polishing fixture. As will be apparent, the precision bore has a precise size, such as to within a tolerance of one micron or so, and a predetermined orientation. While the single fiber ferrule is held by the precision bore of the polishing fixture, the front surface of the single fiber ferrule is brought into contact with the polishing media and polished.
While the outer diameter of a ferrule is an effective datum for cylindrical single fiber ferrules, the exterior dimensions of a multifiber ferrule are not generally defined to within such exacting tolerances since the exterior surfaces of a multifiber ferrule are not referenced in the same fashion as the outer diameter of the cylindrical shaft portion of a single fiber ferrule during the interconnection of a pair of multifiber connectors. In this regard, the outer surfaces of most multifiber ferrules are generally only formed to within tolerances of five microns or more. As such, the exterior dimensions of a multifiber ferrule generally cannot serve as a polishing datum.
Since the exterior surface of a multifiber ferrule does not generally serve as a polishing datum, multifiber ferrules must include other features to serve as a polishing datum. In this regard, the shoulder, or at least portions of the shoulder, defined between the shaft of a multifiber ferrule and the enlarged rear portion of a multifiber ferrule typically serves as a polishing datum. In this regard, the shoulder of a multifiber ferrule is typically formed to be within fairly specific tolerances and to have a predefined relationship with respect to the longitudinal axes defined by the optical fiber bores, namely, a perpendicular relationship with respect to the longitudinal axes defined by the optical fiber bores. However, the shoulder of a multifiber ferrule is typically inaccessible once the multifiber ferrule has been assembled within a connector housing of a multifiber connector. As such, the front face of a multifiber ferrule must typically be polished after the multifiber ferrule has been mounted upon the end portions of a plurality of optical fibers, but prior to assembling the multifiber connector. Since the multifiber ferrule must be mounted upon the end portions of a plurality of optical fibers prior to assembling the multifiber connector, multifiber connectors are not typically assembled in the factory, at which time the assembly process could be efficiently performed in an automated fashion. Instead, a multifiber connector is typically assembled in the field once a technician has mounted a multifiber ferrule upon the end portions of a plurality of optical fibers and the front surface of the ferrule has been polished. As such, polishing the front surface of a multifiber ferrule prior to assembling the multifiber connector decreases the efficiency with which the connector can be assembled and is generally a much less cost effective technique for producing multifiber connectors.
While the exterior surfaces of a multifiber ferrule could be formed more precisely to serve as a polishing datum in much the same fashion as the outer diameter of a cylindrical single fiber ferrule, the manufacture of a multifiber ferrule having precisely formed exterior surfaces would disadvantageously increase the cost of the multifiber ferrule. As such, multifiber ferrules are not generally formed with precisely defined exterior surfaces for use as polishing datums even though the use of such precisely defined exterior surfaces as polishing datums would permit a multifiber connector to be preassembled prior to polishing the front surface of the multifiber ferrule.
As described above, a variety of techniques are available for polishing the front surface of the ferrule. With respect to multifiber ferrules, however, conventional polishing techniques dictate that the front surface be polished after the multifiber ferrule has been mounted upon the plurality of optical fibers, but prior to assembling the multifiber ferrule. In view of the increased costs and inefficiencies incurred to polish the multifiber ferrule in a disassembled state and to then subsequently assemble a multifiber connector including the polished ferrule in the field, it would be desirable to develop other polishing techniques to permit the front surface of a multifiber ferrule to be precisely polished following assembly of a multifiber connector.
A ferrule is therefore provided according to one embodiment of the present invention that includes a ferrule body defining a longitudinally extending groove that can serve as an alignment feature for polishing operations. In this regard, the ferrule body extends longitudinally between opposed front and rear surfaces so that at least the rear surface generally defines a substantially rectangular shape in lateral cross-section. In addition, the ferrule body typically has first and second major sides and first and second minor sides with the first and second major sides being larger than the first and second minor sides. According to the present invention, the ferrule body defines the longitudinally extending groove in at least one of the major surfaces. A jig is also provided according to another embodiment of the present invention for engaging the alignment feature of the ferrule body in order to hold the ferrule in an aligned position during polishing operations. In this regard, the jig includes a jig body that also has an alignment feature for engaging the complimentary alignment feature of the ferrule and a support element having a support surface capable of engaging another side of the ferrule, wherein at least one of the jig body and the support element is capable of pivoting. As such, the front surface of the ferrule can be precisely polished after the ferrule has been assembled into a fiber optic connector since the longitudinally extending groove defined by the ferrule body that serves as the polishing datum is accessible following assembly of the fiber optic connector.
With respect to the ferrule of the present invention, the longitudinally extending groove defined by the ferrule of one advantageous embodiment has a V-shape in lateral cross-section. In this embodiment, the V-shaped groove is truncated such that the groove is defined by a pair of sloping sidewalls and a bottom surface extending between the pair of sloping sidewalls. Regardless of its shape, the groove is preferably defined to extend longitudinally through a medial portion of the respective major surface. In this regard, the ferrule body also typically defines a plurality of optical fiber bores and a pair of guide pin openings on opposite sides of the optical fiber bores. As such, the groove is preferably disposed between the pair of guide pin openings such that the strength and mechanical integrity of the ferrule is not significantly diminished, if at all. In addition, while the ferrule body need only define a single longitudinally extending groove in one of the first and second major surfaces, the ferrule body of one advantageous embodiment defines a pair of longitudinally extending grooves with one groove defined by each of the first and second major surfaces. As such, the ferrule body of this advantageous embodiment is symmetric relative to a plane extending through the optical fiber bores and has a bowtie shape in lateral cross-section.
According to another aspect of the present invention, a polishing jig is also provided that includes an alignment feature for cooperating with the alignment feature of the ferrule to hold the ferrule in an aligned position during polishing operations. In this regard, the alignment features of the ferrule and the polishing jig are selected from a group consisting of a V-shaped alignment groove and an outwardly protruding alignment member having a semicircular shape in cross-section. The alignment features of the ferrule and the polishing jig are therefore selected from the group such that the ferrule includes one type of alignment feature, such as the longitudinally extending groove as described above, and the polishing jig includes the other type of alignment feature.
The polishing jig preferably includes a jig body having a contact element that typically includes the alignment feature, and a support element having a support surface such that the ferrule is held in an aligned position between the jig body and the support element. Typically, one of the support element and the jig body is capable of pivoting about an axis perpendicular to the alignment feature of the jig body to ensure that the ferrule is evenly supported or loaded across its entire surface during the subsequent polishing operations. The support surface of the support element also preferably includes a contact element, such as at least one rib, that protrudes outwardly relative to the other portions of the support surface. By contacting the ferrule with the contact element and not with the other portions of the support surface, the support element of this embodiment of the present invention reduces the contact area and correspondingly reduces the deleterious impact of dirt that may have accumulated on the surface of the ferrule on the resulting alignment of the ferrule within the polishing jig. In one advantageous embodiment, the contact element of the support element includes a pair of parallel ribs. Alternatively, the contact element of the support element can include a T-shaped rib.
The contact elements, such as the alignment feature of the jig body and the ribs of the support element, are preferably sized such that the support elements can be inserted through corresponding openings defined by the connector housing. As such, the polishing jig of the present invention can engage a ferrule following preassembly of the connector. As such, the front face of the ferrule can advantageously be polished following assembly of the connector.
As described above, the alignment feature of the ferrule is typically a longitudinally extending groove. Correspondingly, the alignment feature of the jig is typically an outwardly protruding alignment member, such an alignment rib carried by the jig body and adapted to engage the groove defined by the ferrule. In this regard, the groove defined by the ferrule and the outwardly protruding alignment member carried by the jig body have cross-sectional shapes selected from the group consisting of a semicircular shape and a V-shape. Typically, the ferrule defines a V-shaped groove and the jig body includes an outwardly protruding alignment member having a semicircular shape, although the ferrule can include the outwardly extending alignment member and the jig body can define the V-shaped groove, if so desired.
According to the present invention, the polishing jig can securely hold the ferrule in an aligned position during polishing operations even after the ferrule has been assembled as part of the fiber optic connector. In this regard, by engaging the V-shaped groove defined by the ferrule of one embodiment of the invention with an outwardly protruding alignment rib having a semicircular cross-section, the jig body effectively establishes two lines of contact with the ferrule. In addition, by supporting the opposite side of the ferrule with the support element, a third region of contact is established, thereby insuring that the ferrule is held by the polishing jig in an aligned and secure fashion even after the ferrule has been incorporated into a multifiber ferrule. As such, the longitudinally extending groove defined by the ferrule can serve as the datum during polishing of the front surface thereof, even after the ferrule has been assembled into a connector.